The present invention relates to the fleld of variable delay lines. and more specifically relates to a variable delay line suitable for handling ultra high speed signals, whose delay time can be finely varied over a large number of relatively small steps.
There are currently available conventional type high precision and high speed delay lines, the delay time of which can be varied in the range of from 0 to about 2 ns (nanoseconds) over about 40 or so stages, i.e. by individual steps of about 50 ps (picoseconds), and whlch can handle ultra hlgh speed signals having rise time of 300 ps or less. Such high speed delay lines are typically available in DIP packages. In such typical conventional high precision and high speed delay lines, its delay time can typically be varied at a resolution of about 2.5% of the overall range of delay time, by utilizing a single adjustment mechanism.
However, recently there has made itself felt a growing demand for even finer adjustability of delay time. i.e. for smaller adjustment steps relative to the total delay time range. For instance, it has become desired to achieve a resolution of 1% or finer. However, according to prior art constructions, provision of such a fine adjustability resolution has necessitated the provision of a hundred or more fixed contacts to be switched over between. and this not only increases costs and causes difficulty in manufacture but also means that the device loses its desirable degree of compactness. Further, it becomes very difficult to adjust the delay time of the delay line by using only a slngle adjustment mechanism, when the fineness of the resolution of the delay line is thus increased.